The Drive Behind Mission #3Cool Roofs

The Benefits of Cool Roofs

Photo: Duro-Last Roofing

Cool roofs or light colored, reflective surfaces reflect more sunlight than dark ones, turning less of the sun's energy into heat. Increasing the reflectance of our roofs can can reduce the temperature of buildings, cities and even the entire planet. White roofs, and other cool surfaces, are an efficient and affordable tool to help alleviate some of the stress caused by rising local, regional and global temperatures. A cool roof is a roofing system, consisting of materials of white or light-color, which effectively reflects the sun's energy from the roof surface. Reflective surfaces do not need to be white. The term "cool roofs" is used to exemplify how materials of high solar reflectance come in a range of colors, including many shades of grey and even light red. Learn more.

Significantly cut greenhouse gas emissions and combats global climate change by reducing energy needs and cooling cities and the world. This is done through principles of solar radiation management and geoengineering, which show that cool roofs are not only used to reflect solar energy but emit infra-red radiation to cool the planet and reduce global warming. Learn more.

If all urban, flat roofs worldwide were whitened, the reduction in carbon emissions would be 24 Gigatonnes, or equivalent to taking 300 million cars off the road for 20 years. Learn more.

A study by Lawrence Berkeley National Laboratory showed that if cool roofs were widely adopted, the Greater Toronto metropolitan area could save more than $11 million annually on energy costs. Learn more.

Quick Facts About Cool Roofs

The latest research shows that cool roofs and pavements can help cool the entire planet. Permanently retrofitting urban roofs and pavements in the tropical and temperate regions of the world with solar-reflective materials would have an equivalent effect on global temperatures as stopping the emissions of 44 billion tonnes of CO2, or over one year’s worth of humanity’s CO2 emissions.

Reducing air-conditioning demands in the U.S. by installing cool roofs on 80% of the 2.58 billion square meters of commercial building conditioned roof area could save 10.4 terawatt hours of electricity and $735 million annually.

Pavements and roofs comprise approximately 60% of city surfaces. Cool roofs and cool pavements can help reflect away the sweltering temperatures of summer urban heat islands, improving air quality and comfort. Widespread installations of cool roofs and pavements can reduce summer air temperatures in cities by 2 to 3 degrees Celsius (4 to 5 degrees Fahrenheit).

"In a typical city, pavements account for 35 to 50 percent of surface area, of which about half is comprised of streets and about 40 percent of exposed parking lots. Most of these streets and parking lots are constructed with dark materials. Because dark pavements absorb almost all of the sun’s energy, the pavement surface heats up, which in turn also warms the local air and aggravates urban heat islands.” Like cool roofs, which are lighter-colored roofs that keep the air both inside and outside the building cooler by reflecting more of the sun’s energy, cool pavements reflect as much as 30 to 50 percent of the sun’s energy, compared to only 5 percent for new asphalt (and 10 to 20 percent for aged asphalt)." ~ Heat Island Group, 'Berkeley Lab researchers showcase cool pavement technologies'

"A new study of how different white roofing materials performed “in the field” in New York City over multiple years found that even the least expensive white roof coating reduced peak rooftop temperatures in summer by an average of 43 degrees Fahrenheit. If white roofs were implemented on a wide scale, as the city plans to do, this reduction could cut into the “urban heat island” effect that pumps up nighttime temperatures in the city by as much as 5 to 7 degrees Fahrenheit in the summer, said the study’s lead scientist, Stuart Gaffin of Columbia University." ~NASA

On a sunny summer afternoon the annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C)., according to the EPA. The elevated air temperatures associated with this summer “urban heat island” (UHI) make air conditioners work harder to keep buildings cool, which can strain the power grid. They also accelerate the formation of smog, degrading air quality. Image courtesy of Heat Island Group, Lawrence Berkeley National Laboratory

The "Heat Island" Effect

On May 11-12, 1997, NASA used a specially outfitted Lear Jet to collect thermal data on metropolitan Atlanta, Georgia. Nicknamed “Hot-Lanta” by some of its residents, the city saw daytime air temperatures of only about 26.7 degrees Celsius (80 degrees Fahrenheit) on those days, but some of its surface temperatures soared to 47.8 degrees Celsius (118 degrees Fahrenheit). In this image, blue shows cool temperatures and red shows warm temperatures. Pockets of especially hot temperatures appear in white. Image courtesy of NASA/Goddard Space Flight Center Scientific Visualization Studio

For hundreds of millions of people living in or near cities, urban heat islands are a growing environmental and health concern. If you turn on the local weather report, you'll most likely notice a strange trend. Temperatures are often higher in cities in comparison to their surrounding areas. According to the EPA, the annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C). This is a result of a phenomenon known as the urban heat island effect. "Heat Islands" are mainly caused by dark surfaces, which absorb and hold more heat from the sun, and from less vegetation, which would provide shade and cool the air. Elevated temperatures from urban heat islands, particularly in the summer, affect a communities environment and quality of life. Although the heat island impacts lengthen the plant-growing season, the EPA outlines the many detrimental effects of urban heat islands:

Increased energy consumption: Higher temperatures in the summer increase energy demand for cooling and adds great pressures to the electricity grid during peak periods of demand. One study estimates that the heat island effect is responsible for 5-10% peak electricity demand for cooling buildings in cities.

Elevated emissions of air pollutants and greenhouse gases: Increased energy demands generally result in greater emissions of air pollutants and greenhouse gas emissions from power plants. Higher air temperatures also encourage the formation of ground-level ozone.

Impaired Water Quality: Hot pavement and rooftop surfaces emit massive excess heat to stormwater, which drains into storm sewers and raises water temperatures as it is released into streams, rivers, ponds, lakes and oceans. These rapid temperature changes are stressful and damaging to aquatic ecosystems.

Perhaps the worst result of the heat island effect is the number of heat related deaths. The National Oceanic and Atmospheric Administration reports that heat is usually more deadly in the U.S. and typically kills more people each year than hurricanes, tornadoes, floods and lightning put together.